1. Field of the Invention
The present invention relates to a method and apparatus for detecting, in a water purification process or the like, a flocculation process from flocculant components in a liquid after a flocculant is added into raw water including a plurality of components such as suspended particles or dissolved organic materials.
2. Description of the Prior Art
As is well known, raw water such as water from rivers, lakes and marshes takes a form of a suspension including a plurality of flocculated components. Here, the flocculated components refer to suspended components and dissolved components. A suspension, as is well known, refers to a liquid with suspended solid particles having diameters sufficient to cause light scatter. Suspended components refer to components existing in the raw water in the form of solid particles such as clay. Dissolved components refer to components uniformly mixed into the raw water, such as an acid like humic acid, an alkali, an inorganic salt, etc., and in particular, in this specification, it can refer to dissolved biologically metabolic organic compounds such as humic acid or fulvic acid.
By adding a flocculant into the raw water containing the above described components, these components are flocculated to form flocs. Removing the flocs from the raw water purifies the raw water.
When a flocculant is added into the raw water and stirred, the following components are formed in the flocculation process.
(i) Flocs B+X: When a flocculant is added to raw water, the flocculant is immediately hydrolyzed to form product X. At the same time, a dissolved component B is caught into the hydrolyzed product of flocculant X to form flocs B+X. PA1 (ii) Compound A+B+X: A suspended component A in the raw water is captured into flocs B+X to form a compound (called hetero-flocs below) A+B+X. PA1 (iii) Suspended components A which are not captured into the flocs A+B+X, exist independently in a manner similar to the situation in which no flocculant is added to the raw water. PA1 (iv) Dissolved components B which are not captured into the flocs B+X and hetero-flocs A+B+X, and exist independently in a manner similar to the situation in which no flocculant is added to the raw water. PA1 T: transmittance (I/I.sub.0); PA1 K: a constant determined by the type of suspended particles, a cross sectional area of incident light, and the path length of the incident light; PA1 C: concentration of the suspended particles. PA1 [a] The number concentration of suspended particles decreases as the aggregation proceeds, and at the same time, particle sizes grow larger. Thus, the two parameters (the number concentration and the particle sizes) change so as to cancel each other with regard to turbidity. As a result, it is difficult to obtain direct information about the flocculation process from the turbidimeter. In practice, the conditions for process control are judged by measuring the turbidity after the flocculation process has been completed. Accordingly, a quick feedback control is impossible because it takes a long time to obtain the result of the measurement of the flocculation process. PA1 [b] In the particle counter, basically only one suspended particle is allowed to pass through the beam or pinhole at a time, which is difficult to satisfy because the concentration of the suspension which is treated in the flocculation process is high. Hence, the particles aggregate densely. Accordingly, measuring the concentration of the suspension when it is high using the particle counter requires dilution of the suspension to make a sample liquid. In addition, the information obtained by the particle counter is limited to the concentration of the suspended particles and to the particle-size distribution. Information regarding the flocs produced from the reaction between the flocculating agent and flocculated components cannot be obtained. Accordingly, the means of (b) above cannot detect the flocculation process of the flocculant components in the suspension. PA1 [c] Turbidimetry can use a high concentration suspension without dilution because it measures statistical fluctuation amounts. The information regarding the flocs themselves, however, cannot be obtained by the measurement means. PA1 [d] The means of (d) above determines the concentration of dissolved components from an absorbance measured by the spectrophotometer. Thus, the behavior of the flocculation process cannot be measured. PA1 irradiating a flow of the sample liquid with a beam including at least first and second wavelength components having different wavelengths; PA1 converting with an photoelectric converting means a transmitted beam, which is a part of the beam passing through a flow of the sample liquid, into electric signals each corresponding to the wavelength components; and PA1 calculating using the electric signals intensities of the wavelength components of the transmitted beam, mean values, standard deviations and coefficients of variation of absorbances of the wavelength components, and correlation coefficients between the intensities of the wavelength components of the transmitted beam. PA1 calculating a mean value E.sub.1 of the absorbance of the first wavelength component; PA1 calculating a standard deviation E.sub.r1 of the absorbance of the first wavelength component; PA1 calculating a mean value E.sub.2 of the absorbance of the second wavelength component; PA1 calculating a standard deviation E.sub.r2 of the absorbance of the second wavelength component; PA1 calculating a time serial correlation coefficient .rho..sub.12 between the absorbances of the first and second wavelength components; and PA1 calculating absorbance E.sub.2 ' of an uncoagulated dissolved component which is uniformly contained in the sample liquid without having been adsorbed by particles in the sample liquid by using the following equation (1) and the values E.sub.1, E.sub.r1, E.sub.2, E.sub.r2, and .rho..sub.12. ##EQU1## PA1 a light source for emitting a beam of light including a plurality of wavelength components having different wavelengths; PA1 a flow cell through which the sample liquid flows; PA1 first optical means for transmitting the beam of light and for irradiating the flow cell; PA1 photoelectric converting means for converting a transmitted beam, which is a part of the beam passing through the flow cell through which the sample liquid flows, into electric signals each corresponding to the wavelength components; and PA1 calculating means for calculating from the electric signals, intensities of the wavelength components of the transmitted beam, mean values, standard deviations and coefficients of variation of absorbances of the wavelength components, correlation coefficients between the intensities of the wavelength components of the transmitted beam.
The flocs A+B+X are an object product of flocculation in water purification.
In this specification, the solid particles that come into existence in the flocculation process (i.e., the suspended components A, hydrolyzed product of flocculant X, flocs B+X, and hetero-flocs A+B+X) are called suspended particles.
The following four methods are known as conventional techniques for measuring concentration of suspended particles in a suspension.
(a) A first method obtains the concentration of suspended materials in a sample suspension (a uniform material layer) by Lambert-Beer's law representing the absorption of light when it passes through the uniform material layer, and a turbimeter using this method is also known. Lambert-Beer's Law can be expressed by the following equation (A). EQU -lnT=KC (A)
where
in which
I: intensity of transmitted light; PA3 I.sub.0 : intensity of incident light;
According to equation (A), the concentration C of the suspended particles in the sample liquid can be found by knowing the light transmittance T of the sample liquid. The turbidimeter is arranged in such a way that it can be determined the concentration C by measuring the light transmittance T of the sample liquid and by applying equation (A) to the measured value.
(b) A second method determines the concentration of suspended particles in a sample liquid by measuring the number of particles in the liquid by using a laser. As means for measuring the number concentration of suspended particles in the liquid, the following counters are known: a particle counter that detects laser light scattered by particles; a particle counter based on a light obscuration method, which counts pulses to detect a reduction in the intensity of the transmitted light, this reduction being produced when a beam of light emitted from a laser or an LED passes the particles; and a Coulter counter that detects changes in electrical conductivity of the liquid produced when the particles pass through a pinhole.
(c) A third method is a variation of the first method in which the apparatus used is a kind of turbidimeter disclosed by John Gregory on pages 357-371 of Journal of Colloid and Interface Science, Vol. 105, No. 2, June 1985. This apparatus separates the DC component and AC component of the intensity of the transmitted light, and produces, as an output, a root means square value of the of the fluctuation of the light transmitted through the flowing particles. This makes it possible to calculate an average particle size for monodisperse suspension particles.
(d) A fourth method measures the concentration of soluble organic materials (biologically metabolic organic materials) represented by humin in raw water. Absorbance of ultraviolet light is used as a concentration index of the soluble organic materials (the biological metabolic organic materials). The absorbance of ultraviolet light (260 nm) can be measured by a spectrophotometer.
The information given by the above conventional means is limited to the average concentration of suspended particles in a suspension, particle-size distribution, absorbance, transmittance thereof, or the like. As a result, using the above means for measuring the suspension in the flocculation process in which the suspended particles are being aggregated by a flocculating agent added to the suspension, presents the following problems which will be explained corresponding to the above (a)-(d).